Hereinafter, a scheduling service used in a general radio access system will be described. In addition, a method of requesting a bandwidth will be described.
The scheduling service is a service for requesting an uplink bandwidth and efficiently allocating a resource according to the request. In addition, the scheduling service indicates a data processing method supported by a medium access control (MAC) scheduler when data is delivered by a connection. The connection between a base station and a mobile station is associated with one scheduling service. The scheduling service may be defined by a series of quality of service (QoS) parameters for performing a service operation.
The scheduling service includes outbound transmission scheduling and uplink request/grant scheduling.
The outbound transmission scheduling indicates that a specific frame is selected or a bandwidth is allocated in order to transmit data. The outbound transmission scheduling may be performed by a base station (e.g., in downlink) or a mobile station (e.g., in uplink).
The uplink request/grant scheduling is performed by a base station in order to provide a bandwidth for an uplink transmission to a mobile station or provide an opportunity for requesting a bandwidth to a mobile station. If a scheduling type and QoS parameters associated therewith are specified, a base station scheduler may estimate an uplink traffic throughput and a necessary standby time and provide a poll or a grant at an adequate time.
The uplink request/grant scheduling type includes an unsolicited grant service (UGS) type, a real time polling service (rtPS) type, a non-real time polling service (nrtPS) type and a best effort service (BE) type.
The UGS is designed so as to support a real time uplink service flow for periodically generating a data packet having a predetermined size. For example, the UGS includes a voice over Internet protocol (VoIP) without silence suppression or a T1/E1. In addition, the USG may periodically allocate a slot having a fixed size without a separate contention or request. That is, the USG fixedly allocates a bandwidth to a mobile station so as to guarantee a constant resource.
The rtPS is designed so as to support a real time uplink service flow function for periodically generating data packets having variable lengths, such as a video phone or a moving pictures experts group (MPEG) video. The rtPS may periodically provide real time unicast request opportunities to a mobile station. In addition, the rtPS satisfies a real time requirement of a service flow and allows the mobile station to specify a desired resource size on the basis of the real time requirement. At this time, the mobile station may use a given request opportunity and cannot make a request using contention.
The nrtPS periodically provides a unicast poll function and can guarantee an uplink service flow to receive a request opportunity even in a communication network congestion state. Generally, a base station polls nrtPS connection identifiers (CIDs) at an interval of 1 second or less. The nrtPS is used for burst non-real time data traffic having a variable size, such as file transfer requiring a high bandwidth.
The object of the BE grant scheduling is to provide an efficient service for best effort traffic. The BE service allows a mobile station to use a request opportunity based on contention. Accordingly, the mobile station may use the request opportunity based on contention, a unicast request opportunity and a data transmission opportunity.
In the present specification, among the uplink request/grant scheduling services, for example, the rtPS will be described. Other scheduling services may be used and may be differently applied according to the requirement of a system.
Hereinafter, a bandwidth allocation and request mechanism will be briefly described.
A request function is used by mobile stations in order to inform a base station that the mobile stations require an uplink bandwidth allocation. In a general wideband radio access system, a method of requesting a bandwidth includes a basic request method and a random access request method.
In the basic request method, a mobile station requests an uplink bandwidth allocation in unicast by polling of a base station. In addition, the mobile station may piggyback the residual area of the bandwidth previously allocated by the base station and request an uplink bandwidth.
In the random access request method, a plurality of mobile stations contentiously transmits bandwidth request messages via one uplink channel based on contention such that the uplink bandwidths are allocated.
The polling indicates an MAC scheme for sequentially or periodically checking whether or not data which will be transmitted by devices commonly using one communication line is present. In particular, the polling scheme of wireless communication indicates an MAC scheme for allowing a base station to sequentially check whether or not transmission requests of mobile stations are made and allowing the transmission to the requesting mobile station.
That is, the polling is used to allow a base station to specially allocate uplink bandwidths to mobile stations. The bandwidth allocating method may be performed in the form of a series of information elements (IEs) included in an uplink map (UL-MAP), instead of in the form of a message. Generally, the polling may be performed in the unit of mobile stations. The bandwidth is always requested in the unit of connection identifiers (CIDs) and is allocated in the unit of mobile stations.
FIG. 1 is a view showing an example of a unicast polling method used generally.
The rtPS used in FIG. 1 is an uplink scheduling type service in which a mobile station periodically requests data having a variable size in real time, such as an MPEG video.
Referring to FIG. 1, a base station (serving BS #1) performs unicast polling to a mobile station (MS #1) in downlink to support the rtPS. That is, the base station allocates an uplink resource, which is used by the mobile station for requesting a bandwidth, to the mobile station using a UL-MAP (UL-MAP_IE) message. At this time, the UL-MAP message may be periodically transmitted, and the period thereof may be a value set in a process (dynamic service addition (DSA) process) of generating a service flow (S101).
The mobile station requests the bandwidth corresponding to the size of a data packet, which will be transmitted from the mobile station to the base station, to the base station via the uplink resource allocated in the step S101. At this time, the mobile station may use a bandwidth request (BR) header in order to request the bandwidth (S102).
The base station, which receives the request for the bandwidth for transmitting the uplink data packet from the mobile station, allocates the uplink resource to the mobile station if the bandwidth requested by the mobile station can be allocated (S103).
The mobile station which receives the bandwidth for the uplink area allocated by the base station may transmit uplink data to the base station via the allocated transmission area (S104).
That is, generally, the mobile station which receives the rtPS may request and receive the uplink resource by the procedure shown in FIG. 1.
FIG. 2 is a view showing a resource allocating method for requesting a bandwidth according to the sequence of frames if the number of mobile stations which receive the rtPS is one and an uplink resource allocation period is 2.
In FIG. 2, a horizontal axis shows a frame unit with time and a vertical axis shows a subchannel unit according to a frequency. One frame may include a downlink channel and an uplink channel.
Referring to FIG. 2, a base station allocates an uplink channel (burst) for requesting a bandwidth to a mobile station in downlink at an Nth frame. The mobile station may transmit a BR header to the base station via the uplink channel (burst) allocated by the base station at the Nth frame.
The base station allocates an uplink bandwidth for transmitting data from the mobile station to the base station to the mobile station in downlink at an N+1th frame. The mobile station may transmit data (data burst #1) to the base station via the uplink bandwidth allocated by the base station at the N+1th frame.
The mobile station may subsequently transmit data (data burst #2) to the base station via the uplink bandwidth. At this time, the base station may periodically perform polling. That is, the base station periodically allocates the uplink bandwidth for requesting the bandwidth to the mobile station in downlink. Accordingly, the base station allocates an uplink resource for transmitting a BR header to the mobile station even at an N+2th frame. At this time, if uplink data which will be transmitted from the mobile station to the base station is not present, the bandwidth may not be requested.
In addition, the base station may periodically repeat the process of allocating the resource area for requesting the bandwidth. The mobile station which receives the rtPS by the above-described method may periodically receive the uplink resource allocated by the base station.
FIG. 3 is a view showing another example of the unicast polling method used generally.
FIG. 3 shows an uplink allocating process for supporting the rtPS. At this time, in a base station (serving BS #1), one or more mobile stations which receive the rtPS may exist. In the present specification, it is assumed that two mobile stations (MS #1 and MS #2) which receive the rtPS exist. In FIG. 3, the same reference numerals denote the same steps, and suffixes a and b respectively denote the identifiers of the messages of the mobile stations.
The base station transmits UL-MAP messages including UL-MAP_IE to the first mobile station #1 and the second mobile station #2 in downlink (S301a and S301b).
In the step S301, the UL-MAP_IE included in each UL-MAP message is uplink map information for allocating a resource area for requesting an uplink bandwidth to each mobile station. Since the UL-MAP_IE transmitted to each mobile station has 32 bits, the base station should use 64 bits (32 bits*number of mobile stations) in order to allocate the uplink resource areas to the two mobile stations.
At this time, if the number of mobile stations which receives the rtPS is increased, the base station should allocate the uplink resource areas for requesting the bandwidth to the mobile stations by the increased number of mobile stations. Accordingly, overhead due to the transmission of the UL-MAP messages by the base station is increased in proportion to the number of mobile stations.
If uplink data which will be transmitted from the mobile stations to the base station is present, BR headers (48 bits) are transmitted to the base station via the uplink resource areas allocated to the mobile stations at an Nth frame (S302a and S302b). In the step S302, the BR headers are used for requesting the bandwidth corresponding to the size of data which will be transmitted from the mobile stations to the base station.
The base station receives the BR headers from the first mobile station in the step S302 and the second mobile station and determines whether or not the bandwidths are allocated. The base station transmits UL-MAP (BW allocation) messages including resource area information for allocating the bandwidths to the mobile stations to the mobile stations at an N+1th frame (S303a and S303b).
The mobile stations receive the respective uplink bandwidths from the base station via the UL-MAP messages. Accordingly, the mobile stations may transmit uplink data to the base station via the allocated transmission areas at the N+1th frame (S304a and S304b).
If the uplink data which will be transmitted to the base station is not present, the mobile stations set the BR areas of the BR headers to 0 and transmit the BR headers to the base station. Then, the uplink allocating process is finished and the steps S303 and S304 may be omitted.
At this time, the BR may indicate the size of the data which will be transmitted by the mobile station. The steps S301 to S304 may be performed in a period (or at an interval) set in the process of generating the service flow.
FIG. 4 is a view showing a resource allocating method according to the sequence of frames if the number of mobile stations which receive the rtPS is two and a polling period is 2.
FIG. 4 shows the method of allocating the uplink resource by the method of FIG. 3 according to the sequence of frames. In FIG. 4, the base station (serving BS) transmits the UL-MAP messages including UL-MAP_IE to the first mobile station (MS #1) and the second mobile station (MS #2) at the Nth frame. At this time, the UL-MAP_IE specifies the resource area for requesting the uplink bandwidth to the base station by the mobile station if the data which will be transmitted from the mobile station to the base station is present. The UL-MAP_IE of each mobile station has a size of 32 bits. Accordingly, if two mobile stations are present, the base station uses 64 bits (32 bits*number of mobile stations).
If two or more mobile stations which receive the rtPS are present, overhead which occurs in the base station is increased in proportion to the number of mobile stations when the base station transmits the UL-MAP messages.
Each mobile station may request a bandwidth for transmitting data to the base station via the uplink area received by each UL-MAP message at an Nth frame. At this time, each mobile station may use the BR header.
The base station recognizes the bandwidths required by the mobile stations via the BR headers and allocates the bandwidths to the mobile stations. The base station allocates the uplink bandwidths to the mobile stations via downlink transmission areas at an N+1th frame. In addition, the mobile stations may transmit data to the base station via the allocated uplink bandwidths at the N+1th frame.
The base station periodically allocates the uplink transmission areas for requesting the bandwidths to the mobile stations. For example, in FIG. 4, since the period is 2 frames, the base station may allocate the resource areas for requesting the uplink bandwidths to the mobile stations at an N+2th frame. At this time, if the uplink data which will be transmitted from the mobile stations to the base station is not present, the process of transmitting the data at an N+3th frame may be omitted.
Referring to FIGS. 1 to 4, in a communication environment in which the number of mobile stations which receive the rtPS is increased in a generally used method, the overhead which occurs in the base station is continuously increased in proportion to the number of mobile stations.